Advanced gas turbine engines require alloys exhibiting very high melting points in order to increase performance and operating efficiency. Molybdenum-based alloys have been developed to increase the turbine operating temperature as disclosed in U.S. Pat. No. 5,693,156 to Berczik, U.S. Pat. No. 5,595,616 to Berczik, and U.S. Pat. No. 6,652,674 to Woodard et al., which are all incorporated herein by reference in their entireties. The molybdenum-based refractory metal alloys described therein are attractive candidates to replace nickel-based alloys due to their higher melting point temperatures (approximately 4000° F. to 5000° F.), high coefficients of thermal conductivity (approximately 690 BTU-in/hr ft2-° F.), low coefficients of thermal expansion (approximately 3.5×10−6/° F.), and high modulus. In part, these characteristics are due to these alloys containing constituents with widely varying melting points.
However, the characteristic high temperature capabilities of the aforementioned molybdenum-based alloys also present an obstacle during the production and processing of the alloys. Due to the high melting points and high thermal conductivity coefficients, the molybdenum-based alloys prove to be extremely difficult to melt and cast using traditional processes. Additionally, the mechanical properties of the alloys are highly dependent upon a fine microstructure that cannot be obtained through traditional casting or powder metallurgical processes. As disclosed in U.S. Pat. No. 5,595,616, it was discovered that complete melting and rapid solidification of the melt is necessary to produce the ideal microstructure and subsequent mechanical properties exhibited by these molybdenum-based alloys.
In the past, a widely-recognized process for producing powders of these aforementioned molybdenum-based alloys was rotary atomization as disclosed in U.S. Pat. No. 5,595,616. While rotary atomization was capable of producing usable materials, the process demonstrated limited efficiency. The low efficiency of rotary atomization and the inability of other powder production techniques to produce an ideal powder are directly related to the difficulties present in fully melting the aforementioned molybdenum-based alloy and allowing a homogeneous, fully alloyed liquid to form which could then be rapidly solidified.
Therefore, there is a need for a powder production process capable of efficiently producing powder with the ideal microstructure.